GEOLOGY OF THE REMSEN QUADRANGLE 



II 



The Grenville presents many different facies and below follows 

 a description of the principal types which are represented by 

 different layers. A common type is distinctly marked by alter- 

 nating light and dark bands, the light bands consisting mostly of 

 plagioclase feldspar and quartz, while the dark bands are chiefly 

 biotite mica and hornblende together with garnet. 



Another type is of light gray to greenish gray color and rather 

 fine grained. The principal constituent is augite with a fair amount 

 of anorthoclase and quartz together with several per cent of gra- 

 phite. 



A third type shows a very thin banding, is almost white and is 

 made up chiefly of plagioclase (oligoclase) feldspar with some 

 quartz. 



A fourth type is fine to medium, light colored, and is made up 

 of about 75% of anorthoclase, 20% of quartz and 5% of biotite, 

 magnetite and garnet. 



A fifth type is dark gray micaceous, consisting of about 60% of 

 oligoclase, 25% of biotite mica, 10% of quartz and a little mag- 

 netite and hornblende. 



A sixth type, which is rare, consists "mostly of enstatite (or 

 bronzite) with some quartz. 



A seventh type contains much sillimanite accompanied by 

 anorthoclase, quartz, magnetite and biotite. The sillimanite 

 occurs in long glistening needles visible to the naked eye. This 

 type was observed only near Forestport, where Grenville and 

 syenite rocks are closely associated. 



Accompanying the above described Grenville rocks and inter- 

 banded with them are certain rock types which are presumably 

 igneous in origin. One of these rock types is gray, medium grained 

 and consists of about 50% of feldspar — anorthoclase and oligo- 

 clase — 25 to 30% of quartz, varying amounts of hornblende, 

 hypersthene, biotite mica, magnetite, and a little pyrite, apatite and 

 zircon. Found alone in the field it would be impossible to dis- 

 tinguish this rock from the typical syenite below described. 



Another of these rocks thought to be igneous in origin is black, 

 fine grained and highly banded. It consists chiefly of hornblende 

 (50 to 60%) associated with plagioclase feldspar (30 to 40%) 

 which ranges from oligoclase to labradorite and about 5% of mag- 

 netite. According to the composition the original rock would 

 have been a gabbro. These apparently igneous rocks can in no case 

 be represented as separate areas upon the map. 



Since the rocks of the Grenville series have been so profoundly 



